The invention relates to a circuit arrangement for controlling the transmission capacity of the receiving branch in a full-duplex transmission system which is connected by its transmitting and receiving branches to a two-wire transmission line via a hybrid circuit. An echo compensation network is provided between transmitting and receiving branches of the transmission system and an amplifier is arranged in the receiving branch.
Circuit arrangements of the type referred to above are already generally known (see, for example, "Adaptive Reference Echo Cancellation" by D. Falconer, IEEE Transactions on Communications, Vol. Com. 30, No. 9, September 1982, pages 2083 to 2094; and German patent No. 2,944,486). In these known systems difficulty is experienced when regular operation is resumed following a line break on the two-wire transmission line. When a line break occurs the system echo compensation network functions in such a manner that, for the particular circumstances of the line break, an exact compensation is effected of the signal components which are emitted from the associated transmitting branch so as to prevent cross-talk in the associated receiving branch. When the previously interrupted two-wire transmission line resumes operation, the echo compensation network must first be set in accordance with the changed conditions before data signals emitted from another subscriber station--referred to herein as the "opposite station"--can be satisfactorily received. In this case, in order to prevent that faulty data signals reach a data terminal connected to a transmission system of this type, the data signal reception must be blocked during this last-mentioned compensation process. For this purpose it is possible to use a timer, although a timer cannot determine and duplicate that period of time which corresponds to the actual conditions of the system; namely, the time during which the data signal reception is or will be blocked.